Abstract
Gene transfer vectors derived from gamma-retroviruses or lentiviruses are currently used for the gene therapy of genetic or acquired diseases. Retroviral vectors display a non-random integration pattern in the human genome, targeting either regulatory regions (gamma-retroviruses) or the transcribed portion of expressed genes (lentiviruses), and have the potential to deregulate gene expression at the transcriptional or post-transcriptional level. A recently developed alternative vector system derives from the avian sarcoma-leukosis alpha-retrovirus (ASLV) and shows favorable safety features compared to both gamma-retroviral and lentiviral vectors in preclinical models. We performed a high-throughput analysis of the integration pattern of self-inactivating (SIN) alpha-retroviral vectors in human CD34+ hematopoietic stem/progenitor cells (HSPCs) and compared it to previously reported gamma-retroviral and lentiviral vectors integration profiles obtained in the same experimental setting. Compared to gamma-retroviral and lentiviral vectors, the SIN-ASLV vector maintains a preference for open chromatin regions, but shows no bias for transcriptional regulatory elements or transcription units, as defined by genomic annotations and epigenetic markers (H3K4me1 and H3K4me3 histone modifications). Importantly, SIN-ASLV integrations do not cluster in hot spots and target potentially dangerous genomic loci, such as the EVI2A/B, RUNX1 and LMO2 proto-oncogenes at a virtually random frequency. These characteristics predict a safer profile for ASLV-derived vectors for clinical applications.
Highlights
Transplantation of hematopoietic stem cells genetically modified by retroviral vectors has proven its clinical efficacy in a number of seminal clinical trials for the treatment of severe monogenic disorders [1,2,3,4,5,6,7,8]
Small-scale surveys of integration sites of vectors derived from alpha-retroviruses, such as the avian sarcoma-leukosis virus (ASLV), in different cell types indicated a more random pattern compared to other retroviruses, with a slight preference for transcription units, but no apparent preference for promoters and transcription start sites (TSSs) [17,18,19,20]
SIN-human immunodeficiency virus (HIV) in human hematopoietic stem/progenitor cells (HSPCs), we first analyzed the distribution of integration sites around RefSeq genes in the human genome: integration was annotated as TSS-proximal when occurring in an interval of ±2.5 kb from the TSS of any RefSeq gene, intragenic when occurring inside a RefSeq gene >2.5 kb from the TSS and intergenic in all other cases
Summary
Transplantation of hematopoietic stem cells genetically modified by retroviral vectors has proven its clinical efficacy in a number of seminal clinical trials for the treatment of severe monogenic disorders [1,2,3,4,5,6,7,8]. High-definition mapping of integration sites of vectors derived from the Moloney murine leukemia virus (MLV) and human immunodeficiency virus (HIV) in murine and human cells revealed non-random profiles with a strong tendency to target active regulatory regions for MLV-derived gamma-retroviral vectors [13,14] and transcribed regions for HIV-derived lentiviral vectors [15,16] These integration patterns explain the relatively high risk to deregulate gene expression at the transcriptional or post-transcriptional level observed in pre-clinical, as well as in clinical studies (reviewed in [9]). These results highlight a safer integration profile of alpha-retroviral vectors in human cells, supporting their development as a clinical gene transfer tool
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
